Laminated shoe stiffener



[JAMINATED SHOE STIFFENER Filed Feb. 25, 1935 4 Yg. l i f Patented `Apr. 13, 1937 UNITED p STATES LAMINATED SHOE STIFFENEB Harold S. Miller, Quincy, and Charles P. Maclver,

Newton, Mall., assignors to Beckwith Manufacturing Company, Dover, N. H., a corporation of New Hampshire Application February 25, 1935, Serial No. 8,044

o emma. (ci. ss-'m This invention relates to a laminated shoe stiifener, being more especially concerned with a so-called thermoplastic stiifener such as ycan be incorporated into the toe end portion of a shoe upper in a heat-softened moldable condition and molded to the shape of the last during the pullingover and bed-lasting operations.

The thermoplastic stiifener ofthe prior art is usually a single-ply structure, for instance, a felt 1g impregnated with suitable thermoplastic stiifening compound. In order to realize the desired plasticity and adhesiveness in the heat-softened stiffener to permit its ready conformation to the last and its bonding or integration with the lining and/or doubler fabric of the shoe upper. it has been the practice to use as the stiffening impregnant for the felt or other fibrous base a thermoplastic compound of such high plasticity and adhesiveness at moderately elevated tempernecessarily also became so limp, distortable, and easily wrinkled, as to be spoiled or improperly assembled with the shoe upper, unless carefully handled by the Operator. Moreover, the preferred thermoplastic compounds, suchas rosin compositions, that possess the desired high degree of thermoplasticity and adhesiveness at moderately elevated temperatures are quite friable or brittle and hence fall to impart to the stlener the desired high degree of flexibility, the stiiener blank tending to crack or break when bent to a. sharp angle. y

In accordance with the present invention, we provide a laminated shoe stiffener which, a1- though characterized by its thermoplasticity as a whole at temperatures non-injurious to leather and consonant with ready moldability thereof to the shape of a last during the lasting of a shoe upper with which it is assembled, is nevertheless made up of layers or plies of varying thermoplasticity or response to the heat-conditioning treatment usually applied thereto. More particularly, th'e shoe stiffener of the present invention comprises outer layers of suitable fabric or fibrous material impregnated with a thermoplastic compound of high plasticity and adhesiveness under the usual elevated conditioning temperatures and a layer of thermoplastic compound in between the outer layers of sufliciently lower thermoplasticity to avoid flabbiness in the stiffener under such temperatures. Thus, the outer layers may contain a thermoplastic impregnant of high plasticity and adhesiveness at conditioning temperatures of, say, about 200 to 212 F., whereas the layer of thermoplastic compound in between the atures that the heat-conditioned stiil'ener blank outer layers may be of sufliciently lower thermoplasticity to make for the desired degree of rigidity in the heat-conditioned stiener, that is, a degree of rigidity tending to preserve the heatconditioned stiifener unimpaired while itis being handled and incorporatedv into the shoe upper preparatory to the pulling-over operation. It thus becomes possible to usey rosin compositions to good advantage in the outer layers, since the. lfriable or brittle character'ofA such compositions may be offset in considerable measure by using asv an inner layer the compounds available therefor pog the desired flexibility and so functioning to prevent cracking of the stiifener when it is flexed sharply. By virtue of the fact that the outer layers are substantially completely filled with the external thermoplastic compound, there is little tendency for the inner layer or lm of less thermoplastic stifiening compound to become dissipated by being squeezed into the external layers under the pressure of the lasting operatic In other words, the internal layer of stiiifeningl compound is maintained substantially undisplaced between the two outer plies to impart to the stiifener structure as it appears in the iinishedshoe the desired properties of resiliency and flexibility. The thermoplastic compound present in the outer plies being brought to high plasticity and adhesiveness by the heat-conditioning treatment to which the stiifener blank is subjected serves admirably to bond the stiffener to the lining and/or doubler of the shoe upper.

The principles of the present invention are applicable to especial advantage when the internal layer or lm of stiffening compound is a thermoplastic resin such as is typified by the vinyl ester resins, e. g., polyvinyl acetate, polyvinyl chloride, polyvinyl benzene, etc. Indeed, the vinyl ester resins are so effective that they may/be diluted or compounded with other less expensive materials, as will hereinafter appear, and still give excellent results. We have found that polyvinyl acetate, for instance, lends itself to being laid as a preformed film or spread in plasticized condition in between the outer fibrous layers of the multi-ply stlffener structure of the present invention. Accordingly, the polyvinyl acetate or other polyvinyl resin as a preformed film can be bonded to the outer layers or can be applied in plastic condition by calender rolls or other spreading means in between the outer layers. The three-ply sheet may then be impregnated with a thermoplastic stiening compound suitable for the outer layers, for instance, rosin, a rosin-bitumen mixture, or a rosin-bitumen-wax mixture. To this end, the composite sheet may be immersed in a bath of the thermoplastic compound which, as already indicated, has a thermoplasticity distinctly greater than that oi' the internal layer or lm of polyvinyl resin. The resulting impregnated product .can v'then be cut into shoe stieners.

. In the accompanying drawing the ilgure represents an unskived box toe blank. Y The legends on the drawing designate the composition of the various layers. It will, of course, be appreciated that 'a corner of onel of the outer layers is shown pulled `away from the internal layer and that part of such latter layer is shown broken away for the purpose of exposing each of the layers. The margins of the box toe' sheeted, or being calendered onto textile fabric.A

Upon evaporation of the volatile plasticizing mixture-` from the sheeted. or calendered layer, a. highly flexible illm or. layer resembling celluloid in its flexibility, appearance, and other characteristics results. l

In the case of our preferred stidener containing vinyl resin compound as the internal layer-or film, the more thermoplastic stiifening compound in the outerlayers or plies serves the added important function of preventing access of perspiration orfexternal moistureto such internal layer, which, when absorbed by such layer, detracts from the qualities of ilexibility and resiliency otherwise afforded by suclr layer. In this connection, it might be observed that the internal layer of vinyl resin compolmd has some amnity for moisture, but the waterproofing stiening agent present in the outer plies prevents access of moisture thereto and its deterioratingieffects on the stiifener. 1

A specific example such as may be adopted advantageously in producing a kmulti-ply shoe stiiener embodying the present invention may be substantially as follows. 500 parts by weight of f vinyl acetate may be put into an internal mixer such as is used in rubber compounding, e. g., a Werner and Pfleiderer or a. Banbury machine. The polyvinyl, acetate may be of the alcohol-solvent variety and have a softening point ranging from about 212 F. to 300 F. About 100 parts by weight of ethyl alcohol may be added to the charge in the mixer and mixing may be eected until all lumps of vinyl acetate have disappeared. About 200 parts by weight of M-grade rosin having a melting point of 175 F. may then be added to the mixer along with 100 parts by weight of a. white pigment, such as lithopone, and the charge' allowed to mix until a homogeneous mass results,

whereupon water may be added to the mass and mixing continued until no more water is absorbed thereby. Depending upon the temperature of the mass and, accordingly, the evaporation of water caused thereby, about'100 to 200 parts by weight of water may be added. Sufficient alcohol, say, about 50 parts by weight, may then be added to the operating mixer to bring the mass to the de- 75 sired plasticity vfor sheeting or calendering. At

this stage, the mass has s dougnmke plasticity or consistency and is so elastic and stretchable that it can be drawn out into filaments. At such consistency, the mass can be readily calendered in between' two layers of fabric progressively fed into the nip of a pair of calender rolls, such mass being maintained as a bank-at the intake of the rolls `and being-drawn outorrattenuated in the nip of the rolls as a layer., or film of predetermined thickness, for instance, a thickness ranging from about 0.002 inch t0 0.010 inch. 'Ihe mul- 'the sheet comes oil' the drier rolls, it can be passed through a bath of molten thermoplasticcompound comprising largely rosin, compounded,

yif desired, with such other thermoplastic materials as bitumen, Montan wax, carnauba waxfetc.

' Whereas the polyvinyl resincompound introduced as `the inner layer in the resulting multiply sheet has a softening point'of Vabout 190 F.. the molten thermoplastic compound occurring in the external plies preferably has a. melting point of about 175? F.' Itis thus 'seen'thatthe internal thermoplastic layer is of `decidedly lower thermoplasticity than the impregnant of the outer layers, sinceA such impregnant has a melting point lower than even the softening Point of the internallayer; v

It is preferable that a coarsely Vwoven cotton fabric be used as the outer' ply material of the stiifener, as such a layer can be chargedwith the desired amount of external stiifening'composition. Thus, so-called unsized gray goods approximating four yards tothe pound and of 28 x 32 yar-n count per inch serves admirably as the outer ply material. If desired, however. the outer plies may be other than woven ones. such as water-laid or air-laid felts; andthey might be formed by depositing ilber flock onto a preformed layer or film ofthe vinyl resin compound while the layer is still in a sticky or unset condition, lwhereupon such plies may be im-` pregnated with the appropriate external stifi'en'- ing compound.

The principles of the present invention extend to the use of thermoplastic compounds other than vinyl resins for forming the internal layer or film, although, as alreadyindicated, the vinyl resins are preferred for this purpose. Thus, the internal layer may be a rubber compounclmoldahle underelevated temperature non-injurious to the shoe upper but of distinctly lower thermoplasticity than the Vstiilfening agent carried bythe external fibrous plies. Artiilcial resins of suitable thermoplasticity other than the vinyl resins may be employed, the acrolein resins (Acrolyte) the styrol resins, the glyptol resins, and others falling into this category. I

' Rather than impregnating the plied sheet with rosin or other suitable external stiifening compound, the fabric or ibrous sheet to constitute the outer Vplies may be initially impregnated with rosin or equivalent compound andV two such sheets thus impregnated progressively delivered to the calendering rolls and the rollsA Operated to lay or spread the plasticized polyvinyl acetate or other polyvinyl resin compound in between such pre-'stiened sheets, the internal layer being sumciently adhesive orY plastic to bond teready moldability thereof to the shape of a lastv during thelasting of a shoe upper with which it is assembled, comprising outer layers of fibrous material impregnated and substantially completely filled with a thermoplastic compound of high plasticity and adhesiveness under such temperatures and a layer of essentially only thermoplastic compound in between said outer layers of distinctly lower thermoplasticity than said first-named compound, said in-between layer of compound having little tendency to become dissipated in said layers of fibrous material when said thermoplastic compound in said layers hasl been brought thermally to high plasticity and adhesiveness. f

2. A laminated shoe stiffener characterized by its thermoplasticity, as a whole, at temperatures non-injurious toleather and consonant with ready moldability thereof to the shape of a last during the lasting of a shoeupper with which it is assembled, comprising outer layers of fibrous material impregnated and substantially completely filled with a thermoplastic compound of high plasticity and adhesiveness at temperatures of about 200 tially only thermoplastic compound in between said outer layers of distinctly lower thermoplasticity than said first-named compound, said inbetween layer of compound .having little tendency to become dissipated in said layers of fibrous material when said thermoplastic compound in said layers has been brought thermally to high plasticity and adhesiveness.

3. A laminated shoe stiffener characterized by its thermoplasticity, as a whole, at temperatures non-injurious to .leather and consonant with ready moldability thereof to the shape of a last -during the .lasting of a shoe upper with which it is assembled, comprising outer layers ofl fibrous material impregnated and substantially completely illled with -a rosln composition having a melting point of about 175 F. and a layer of 55 essentially only thermoplastic compound in between said outer layers of distinctly lower therto 212 F. and a layer of essenmoplasticity than said first-namedcomposition, said in-between layer of compound having little tendency to become dissipated in said layers of 'iibrous material when said rosln composition in .material impregnated and substantially completely filled with a thermoplastic compound of high plasticity and adhesiveness at temperatures of about 200 to 212 F. and a substantially berfree layer of polyvinyl resin compound in between said outer layers of distinctly lower thermoplasticity than said ilrst-named compound. said in-.between layer of polyvinylresin compound havingl little vtendency to become dissipated in said layers of thermoplastic compound in said layers has been brought thermally to high plasticity and 4adhesiveness.

5. A laminated shoe stiifener characterized by its thermoplasticity, as a whole, at temperatures non-injurious to leather and consonant with ready moldability thereof to the-shape of a last during the lasting of a shoe upperwith which it is assembled, comprising outer layers of fibrous material impregnated and substantially completely filled with a rosln composition and a substantially fiber-free layer of polyvinyl resin compound in between saidv impregnated outer layers and having qa thermoplasticlty lower than said rosln composition, said in-between layer of polyvinyl resin compound having little tendency to become dissipated in. said layers of brous material when said rosln composition in said layers ,has been brought thermally to high plasticity in between said outer layers having a softening point higher than about 200 F.

HAROLD S. MILLER. CHARLES P. MAcIVER.

fibrous material when said 

